Cylinder bores out of round - how much a acceptable?

[Thuppu]

Is 0.01-0.02mm acceptable? Where goes the line?

[UrS4boy]

Is 0.01-0.02mm acceptable? Where goes the line?

Maximum is 0.08 mm as per page 36/93 in this:

http://s2-audi.co.uk/workshop/aan/aan.pdf

[Thuppu]

I was thinking that was the wear limit of the bore..? But the manual don't say anything about the roundness(and about the shape if bigger in the other end and smaller in the other, don't know the word for this, conical?), so maybe the same specs is for that also?

[UrS4boy]

I was thinking that was the wear limit of the bore..? But the manual don't say anything about the roundness(and about the shape if bigger in the other end and smaller in the other, don't know the word for this, conical?), so maybe the same specs is for that also?

Read pg 36/93 again. It basically says: Measure in 3 locations (as specified). Measure "A" and "B" in those three locations. Compare all six values. Maximum overall deviation between the narrowest and the widest values = 0.08 mm.

Done.

[Thuppu]

Ok, I see that now more clearly, thanks. Isn't 0.08mm quite much?

[elaw]

If I can nitpick on one thing...

The text in the manual states "Deviation from nominal dimension: max. 0.08mm". The way I read that, it's not max. 0.08mm deviation between all the measurements, but rather that none of the measurements can be more than +/- 0.08mm from the cylinder bore spec, which is shown as 81.01mm on the next page (for zero oversize). So I'd say all the measurements should be between 80.93 and 81.09mm.

Also note that the manual says not to measure the bores when the engine is mounted on a repair stand, as it could affect the readings. Of course it doesn't tell you what the engine *should* be mounted on when measuring!

[pasbogdan]

Where on bore you get the 0.02mm?It is wear on the top or out of round?Did you measured bores when they were bored and honed?I found a big important shop here that made me 81.5mm bores 0.02mm out of round.My luck was they made clearances for stock pistons not for fpc.Honed again with new honing stones and it was 0.005mm..

[pasbogdan]

Also note that the manual says not to measure the bores when the engine is mounted on a repair stand, as it could affect the readings. Of course it doesn't tell you what the engine *should* be mounted on when measuring!

It will not change anything in 0.01 sizes.Not even torqued head gets distorsions that you see with a 0.01mm gauge.Done that with stock bolts.Maybe arp will be different story...

[Thuppu]

Where on bore you get the 0.02mm?It is wear on the top or out of round?Did you measured bores when they were bored and honed?I found a big important shop here that made me 81.5mm bores 0.02mm out of round.My luck was they made clearances for stock pistons not for fpc.Honed again with new honing stones and it was 0.005mm..

Out of round, and it's stock bore, driven about 280k km.

[pasbogdan]

Strange...Usualy they are perfect round at bdc and weared at tdc.If you have a block with 0.02mm wear at tdc with 280k you should make a topic with it.It will be my and many others to see such thingSo still in perfect shape.
You use a 2 point or a 3 point bore gauge?

[UrS4boy]

If I can nitpick on one thing...So I'd say all the measurements should be between 80.93 and 81.09mm.

If you are going there, which I don't think is correct, then the readings would have to be between 80.98 mm and 81.08 mm, i.e. a potential difference between minimum and maximum of 0.16 mm - which seems high.

[Thuppu]

Strange...Usualy they are perfect round at bdc and weared at tdc.If you have a block with 0.02mm wear at tdc with 280k you should make a topic with it.It will be my and many others to see such thingSo still in perfect shape.
You use a 2 point or a 3 point bore gauge?

Of course it has wear. Overall wear is like 0.03-0.05mm. Just asking what is the tolerated out of roundness..? 2 point gauge, otherwise I can't see the roundness.

[Error404]

Thomas if its just a thrown together engine for daily duties I wouldn't worry at all about 0.02 out of round

As JP told me "You worry too much"

[repo]

Is Your bore gauge like this:

http://diesunlimited.tradeindia.com/mitutoyo-bore-gauge-917460.html

or this:

http://www.directindustry.com/prod/m...79-666289.html

As first one repeats really well, latter reallyreally does not.

And first one will measure roundness just fine.

[Thuppu]

It's like the first one with a gauge. Should be a pro tool, did loan it from work just for checking the bores.

Did also measure the pistons, with a micrometer. They where 0.01-0.02 under nominal measures, so should be in specs.